An optical Bragg grating coupler is an optical device that has a periodic refractive index variation of the refractive index. For a band of wavelengths around a central wavelength λR, where λR satisfies a phase-matching condition, λR=Λ(n1+n2), and where Λ is the pitch of the grating, and n1, n2 are the effective refractive indices of the modes in the grating, the band of wavelengths incident upon the Bragg grating coupler are reflected. Wavelengths outside the band of wavelengths continue to propagate in the original direction.